Single-component foam systems, particularly those based on a polyisocyanate, consist of a prepolymer which is foamed with a blowing agent, for example a halo-alkane such as Freon R-12. The uncured foam is reasonably stable and is cured by reacting the prepolymer with atmospheric moisture diffused therein.
The reaction mixtures for single-component foams have so far been prepared by two methods:
(1) The prepolymer is prepared in a pressure chamber and then displaced with blowing agent. The reaction mixture is then introduced into a pressure container provided with a valve. The valve must be cleansed in a subsequent operation. This method is mainly used for filling large pressure containers. PA1 (2) Smaller pressure containers (capacity 1 liter or less) are charged with the valves removed therefrom. The reaction components are introduced into an open pressure container, the container is closed with the valve, and blowing agent is added. The container is subsequently shaken.
The first method needs expensive equipment and is slow. It is also difficult to cleanse the chamber installation. Using the second method, the contents of the containers are frequently not mixed sufficiently and lumps are formed which block the valve.